The invention pertains to a device for changing the control timing of gas exchange valves of an internal combustion engine, which is particularly advantageous for application in hydraulic camshaft adjusting devices of the rotary piston type.
A device of this type is known from German patent DE 198 08 619 A1, which generally defines this class. This device, designed as a so-called vane-cell positioning device is formed essentially of a drive gear directly connected to a crankshaft of the internal combustion engine and an impeller that is directly connected to a camshaft of the internal combustion engine. The drive gear has a cavity formed by a hollow cylindrical perimeter wall and two sidewalls, inside of which four hydraulic working chambers are formed from four boundary walls. The impeller has at the perimeter of its wheel hub four vanes, each of which extends radially into a working chamber of the drive gear. These four vanes divide each of the working chambers into two counteracting hydraulic pressure chambers. By selectively or simultaneously applying pressure using a hydraulic pressure medium, these pressure chambers effect a pivoting motion or a fixing of the impeller with respect to the drive gear, and thus the camshaft with respect to the crankshaft. The pressure medium feed to and from the pressure chambers of this device is done by means of a pressure medium tap lying at the axial side of the wheel hub of the impeller facing the camshaft, which is designed as a specialized pressure medium adapter, from a camshaft bearing in the cylinder head of the internal combustion engine. It is also done using pressure medium channels incorporated into both axial sides of the wheel hub of the impeller. These pressure medium channels are connected to the pressure medium tap through a pressure medium distributor penetrating the impeller along its longitudinal axis that is designed in this device as a specialized pressure medium feed bushing. One end of the bushing lies against the axial side of the wheel hub of the impeller that is facing away from the camshaft. The pressure medium tap and the pressure medium distributor are, just as the impeller is, directly bolted to the camshaft by means of a central fastening screw and are each partially enclosed at the head and at the outer surface by a coaxial penetration in the side walls of the drive gear. The gap between the head of the pressure medium distributor and the penetration in the one side wall of the drive gear is sealed against external pressure media leakage by an O-ring in an annular notch in the head of the pressure medium distributor, whereas the gap between the outer surface of the pressure medium tap and the penetration in the other side wall of the drive gear is designed as a sealing gap.
The disadvantage in this known device is that, on the one hand, relatively large play must exist between the head of the pressure medium distributor and the penetration in the one side wall of the drive gear as well as between the outer surface of the pressure medium tap and the penetration in the other side wall of the drive gear so as to prevent a bearing site from occurring at these places. On the other hand, however, the external pressure medium leakages through the gaps at these places are limited, mainly so that less pressure medium has to be fed in the controlled positions of the camshaft-adjusting device. In practice, the O-rings used and the sealing gaps have proven to be unsuitable as a means to seal gaps since the pressure medium channels to the pressure chambers of the device are incorporated into the axial sides of the wheel hub of the impeller. Thus, the pressure of the pressure medium is felt repeatedly at the perimeter of the gaps depending on the number of pressure chambers. As a result, in sealing gaps, the external pressure medium leakages are always still too high, whereas O-rings are so highly compressed by the pressure of the pressure medium that the friction between the pressure medium distributor and the side wall of the drive gear increases. This then leads to higher wear of the O-rings and in the worst case to a worsening of the adjustment speed of the camshaft-adjustment device. Moreover, O-rings have also been shown to be disadvantageous with respect to their embrittlement at high and low temperatures as well as with respect to their incidence of tears and other damage.
The object of this invention is to provide a device for changing the control timing of gas exchange valves of an internal combustion engine, in particular a hydraulic camshaft adjustment device of the rotary piston type, whereby the disadvantages of the known state of the art, are avoided, such as the external pressure medium leakages through the gap between the head of the pressure medium distributor and the penetration of the one side wall of the drive gear and between the outer surface of the pressure medium tap and the penetration of the other side wall of the drive gear are reduced to a minimum.
According to the invention, this object is met by a device in that the gap between the head of the pressure medium distributor and the penetration of the one side wall of the drive gear and between the outer surface of the pressure medium tap and the penetration of the other side wall of the drive gear are sealed off against pressure medium leakage using wear-resistant sealing media.
In a first advantageous embodiment of the device according to the invention, these sealing media are provided preferably as slitted steel sealing rings or as lamellar sealing rings which are each placed in a circular radial notch in the head of the pressure medium distributor and in the outer surface of the pressure medium tap.
Here, the pressure medium distributor is preferably formed from a specialized pressure medium guide bushing that coaxially penetrates the impeller. This feed bushing has at one end a bushing head in which the one radial circular notch for the steel or lamellar sealing ring is located. On the other hand, the pressure medium tap is preferred to be formed by a pressure medium adapter placed onto the other end of the pressure medium feed bushing. It has in its outer surface the other radial circular notch for the steel or lamellar sealing rings. With the help of a central fastening screw passing through the pressure medium feed bushing, the pressure medium tapped from the pressure medium adapter, for example directly from a camshaft bearing in the cylinder head of the internal combustion engine, can on the one hand be thereby passed on along the outside and on the other hand along the inside of the pressure medium feed bushing in respective circular channels incorporated into the axial sides of the wheel hub of the impeller. These channels are connected to the pressure chambers of the device through other pressure medium channels on the wheel hub of the impeller.
However, it is also possible to form the pressure medium distributor, instead of through a specialized pressure medium feed bushing, by the fastening screw itself, drilled out axially hollow, and to incorporate one of the radial circular notches for the steel or lamellar sealing rings into the head of this screw and/or instead of a specialized pressure medium adapter to design the drive end of the camshaft itself as a pressure medium tap. The other radial circular notch for the steel or lamellar sealing rings is then located in its outer surface. The pressure medium feed to the pressure chambers of the device is done in the same manner as in the described design described previously, wherein the pressure medium tap for both designs can come not only directly from a bearing of the camshaft, but also indirectly from another non-rotating pressure medium feed at the cylinder head of the internal combustion engine. Independent of the respective design of the pressure medium distributor and the pressure medium tap, it is moreover also possible to incorporate the surrounding radial circular notches for the steel or lamellar sealing rings into the respective coaxial penetrations in the sidewalls of the drive gear. In the preferably used slitted steel sealing rings, those with straight, slanted or overlapping joints as well as those with cylindrical or hooked joints can be used, with the latter being characterized by an increase in density. The cross sections of the steel sealing rings are preferred here to be square, trapezoidal, round or oval, where the contact surfaces of the steel sealing rings can be designed flat or round. In contrast, depending on the required density, either simple lamellar sealing rings as well as double or multiple layer sealing rings can be used. It is, however, also possible to use un-slitted sealing rings, in particular those made of plastic or similar, as wear-resistant sealing media in the radial circular notches.
As a second advantageous form of the device according to the invention, it is moreover suggested that the sealing media be preferably provided as circular sealing washers that cover the gap between the head of the pressure medium distributor and the penetration in the one side wall of the drive gear and between the outer surface of the pressure medium tap and the penetration in the other side wall of the drive gear by placing them into corresponding circular axial notches. The circular axial notches for the sealing washers are formed by machining out recesses in the penetrations of the sidewalls both at the head of the pressure medium distributor and at the outer surface of the pressure medium tap.
In this embodiment, as well, it has proven advantageous to construct the pressure medium distributor as a pressure medium guide bushing that coaxially penetrates the impeller with a bushing head, on whose axial surface lying against the wheel hub of the impeller a recess is machined that forms one part of the one axial circular notch. In using a hollow-drilled fastening screw as the pressure medium distributor, which is also possible here, the recess forming one part of the circular axial notch can be incorporated into the axial surface of the screw head lying against the wheel hub of the impeller in an equivalent manner. The other part of the circular axial notch is, however, formed from a complementary recess in the penetration of the one side wall of the drive gear encircling the bushing head, independent in either case of the design of the pressure medium distributor. A recess incorporated into the penetration of the other sidewall of the drive gear in the same manner forms one part of the other circular axial notch, moreover, whereas the complementary other part of this circular axial notch is formed into the axial surface of a specialized pressure medium adapter, also preferred to be used as a pressure medium tap here, which lies against the wheel hub of the impeller. It can also be formed into the axial surface of the drive end of the camshaft itself.
The circular sealing washers used in this embodiment are preferably made as steel sealing washers with a square cross sectional profile. However, sealing washers made of other materials, such as sintered steel, cast iron brass, copper, aluminum, plastics, Teflon or the like can be used with trapezoidal, round or oval cross sectional profiles. It is also possible to provide the circular sealing washers with surface treatments or layers by selective phosphating, ferro-oxidation, tinning, copper plating, nitrating, nitrocarborization, chromating or by molybdenum or plastic layering. These layers can also be designed as metallic, ceramic or metal-ceramic mixed layers. Also, those types of devices should be included under the protective scope of the invention that are a combination of the first and second embodiments described used as the sealing medium. Moreover, the invention is suitable not only for installation in any kind of rotary piston positioner, but also for those types of camshaft adjusters that pertain to the principle of an orbiting slow-moving hydromotor.
Thus, the device designed according to the invention to change the control timing of gas exchange valves of an internal combustion engine, in particular a hydraulic camshaft adjustment device of the rotary piston type, has, in both suggested embodiments, the advantage as compared to devices known from the state of the art in that by using wear-resistant sealing rings or sealing washers, the external pressure medium leakages through the gap between the head of the pressure medium distributor and the penetration of the one side wall of the drive gear and between the outer surface of the pressure medium tap and the penetration of the other side wall of the drive gear are reduced considerably. This has the advantage in that to hold the camshaft adjustment device in its controlled position, less pressure medium has to be fed and that at the same time its stability increases since the friction between the sealing rings or sealing washers and their contact surfaces is considerably less than previously known O-rings, in particular at higher compression at the tolerance limits. Moreover, the sealing rings or sealing washers arranged according to the invention make installation of the device easier since they can not twist when installed, in contrast to O-rings, and in addition are subject neither to tears or other damage nor to embrittlement at high or low temperatures.